The present invention relates generally to a scale apparatus for weighing materials moving on a conveyor belt. More particularly, the invention relates to a scale apparatus that can be easily incorporated into existing conveyor systems.
It is often desirable to measure the mass flow rate of material moving on a conveyor belt. By combining the weight of the material and the speed of the conveyor belt, a continuous indication of the mass flow rate of the material moving on the conveyor belt can be generated. Various types of devices are known for measuring the weight of material moving on a conveyor belt.
It is known to provide load cells situated below a conveyor belt to generate an output signal proportional to the weight of a load moving across a conveyor belt. See, for example, U.S. Pat. No. 3,478,830; U.S. Pat. No. 3,439,761; U.S. Pat. No. 3,785,447; U.S. Pat. No. 3,924,729; U.S. Pat. No. 4,682,664; U.S. Pat. No. 4,788,930; U.S. Pat. No. 4,463,816; and U.S. Pat. No. 4,557,341. Conventional belt scales are often large, bulky devices which are expensive and often hard to install. Therefore, many conventional belt scale devices are too expensive for many businesses to purchase and install. Smaller businesses also have a need for reliable measurement of the weight or mass flow of material on a conveyor. For instance, concrete facilities and farming or grain handling facilities often need to know the amount of material moving on a conveyor. The present invention provides an accurate yet inexpensive scale apparatus that can be easily incorporated into existing belt conveyor systems.
If the material carried by the conveyor approaches the load cell from a position above or below the load cell, the materials may impose a side load or torque on the load cell in addition to the loads in the vertical direction. Such side torque can cause the load cell to experience excessive wear and cause inaccuracies in the output of the load cell. Therefore, it is advantageous to arrange the load cell so that the conveyor belt is substantially level as the conveyor belt passes over the load cell. The present invention includes a modular scale unit that provides an aligned and pre-leveled load cell. The scale unit is easily installed in an existing conveyor frame.
According to the present invention, a scale apparatus is provided for weighing material moving on a conveyor belt supported by an idler assembly. The apparatus includes a load cell support and a load cell. The load cell includes a base and a contact portion extending upwardly away from the base. The base of the load cell is configured to bend in response to a vertical force being applied to the contact portion to generate an output signal proportional to the force. The load cell is non-responsive to horizontal forces. The belt scale apparatus also includes means for coupling the load cell to the load cell support and means for coupling the load cell support to a conveyor frame to suspend the load cell below the conveyor belt. The apparatus further includes an idler support for supporting the idler assembly and means for coupling the idler support to the contact portion of the load cell. The idler support applies a downwardly directed force to the contact portion of the load cell to bend the base of the load cell in response to material moving on the conveyor belt over the idler support to change the output signal generated by the load cell in proportion to the weight of the material. The magnitude of the force applied by the idler support changes as the weight of the material moving over the idler support changes.
In one embodiment of the invention, the load cell support is formed to include a central aperture therein for receiving the contact portion of the load cell therethrough. In another embodiment, the load cell support includes a top surface, and the means for coupling the load cell to the load cell support includes a first fastener for coupling a first end of the load cell to the top surface of the load cell support and a second fastener for coupling a second end of the load cell to the top surface of the load cell support. First and second shims are located between the load cell and the top surface of the load cell support adjacent the first and second ends of the load cell, respectively, to elevate the load cell above top surface of the load cell support to permit the base of the load cell to bend. The top surface of the load cell support is formed to include a recessed portion located below the load cell to permit further bending of the load cell.
According to another aspect of the invention, the idler support includes a top surface, a bottom surface, and an aperture extending between the top and bottom surfaces. A fastener extends through the aperture in the idler support for coupling the load cell to the bottom surface of the idler support. The bottom surface of the idler support is formed to include a recessed portion positioned over the contact portion of the load cell.
According to yet another aspect of the present invention, the base of the load cell is formed to include a plurality of notched sections therein to increase the flexibility of the base. The load cell includes a plurality of strain gauges. One strain gauge is located below each of the plurality of notched sections for generating the output signal in response to bending or deflection of the base.
According to still another aspect of the present invention, the belt scale apparatus further includes means for adjusting the level of the load cell support relative to the conveyor frame. The adjusting means preferably includes means for independently adjusting the level of a first end of the load cell support relative to a first side of the conveyor frame and a second end of the load cell support relative to a second side of the conveyor frame. In one embodiment, the means for coupling the load cell support to the conveyor frame includes a first coupler plate for coupling a first end of the load cell support to a first side of the conveyor frame and a second coupler plate for coupling a second end of the load cell support to a second side of the conveyor frame. The means for adjusting the level of the load cell support relative to the conveyor frame illustratively includes at least one shim configured to be selectively positioned between the first coupler plate and the first end of the load cell support, between the first coupler plate and the first side of the conveyor frame, between the second coupler plate and the second end of the load cell support, or between the second coupler plate and the second side of the conveyor frame. By selectively placing the shims, the position of the load cell idler station can be adjusted so that it is aligned with idler roller stations both upstream and downstream from the load cell idler station on the conveyor frame. The shims can be selectively placed either to raise or to lower the load cell support on either side of the attachment of the load cell support to the conveyor frame.
The belt scale apparatus of the present invention is easily installed into existing conveyor systems without substantial modification of the conveyor system. The present invention therefore advantageously provides an inexpensive yet accurate belt scale apparatus for weighing materials passing over the apparatus on a conveyor belt.
According a further aspect of the invention, a scale apparatus is provided for weighing material moving in a downstream direction on a conveyor belt supported by a conveyor frame. The apparatus includes an upstream idler station, a downstream idler station, and a measuring idler station situated between the upstream idler station and the downstream idler station. The apparatus also includes means for measuring the weight of material moving on the conveyor belt. The measuring means is coupled to the measuring idler station. The apparatus further includes means for coupling the upstream idler station, the measuring idler station, and the downstream idler station together to form a scale unit, and means for coupling the scale unit to the conveyor frame so that the conveyor belt passes over the upstream idler station, the measuring idler station, and the downstream idler station.
In the illustrated embodiment, the means for coupling the upstream idler station, the measuring idler station, and the downstream idler station together to form the scale unit includes first and second alignment bars coupled to opposite end portions of the upstream idler station, the measuring idler station, and the downstream idler station. The means for coupling the scale unit to the conveyor frame includes a first set of coupler plates for coupling a first side of the scale unit to a first side of the conveyor frame and a second set of coupler plates for coupling a second side of the scale unit to a second side of the conveyor frame.
Also in the illustrated embodiment, the measuring means includes a load cell coupled to the measuring idler station. The load cell includes a base and a contact portion extending upwardly away from the base. The base of the load cell is configured to bend in response to a force being applied to the contact portion to generate an output signal proportional to the force.
According to an additional aspect of the present invention, the measuring idler station includes a load cell support, means for coupling the load cell to the load cell support, an idler support for supporting an idler assembly thereon, and means for coupling the idler support to the contact portion of the load cell. The idler support applies a downwardly directed force to the contact portion of the load cell to bend the base of the load cell in response to material moving on the conveyor belt over the idler support to change the output signal generated by the load cell in proportion to the weight of the material.
According to another aspect of the present invention, the upstream idler station, the measuring idler station, and the downstream idler station each include a top surface for supporting an idler assembly thereon. The means for coupling the upstream idler station, the measuring idler station, and the downstream idler station together to form the scale unit aligns said top surfaces to lie substantially in a single plane.
In a second embodiment of the scale apparatus, the scale unit includes a second measuring idler station situated adjacent first measuring idler station and second means for measuring the weight of material moving along the conveyor belt. The second measuring means is coupled to the second measuring idler station. The apparatus further includes means coupled to the first and second measuring means for averaging the weight of material measured by the first and second measuring means.
By leveling the scale unit into a planar array of idler stations, the present invention provides a modular scale apparatus that reduces the occurrence of side torque forces on the measuring station and provides a more reliable and accurate scale apparatus. Furthermore, because the scale unit is a single preleveled and aligned unit, the modular scale apparatus of the present invention facilitates installation of the apparatus into an existing conveyor system.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.